Due to gases that are produced by rotary kilns during many chemical processes and that should not be allowed to mix with the surrounding atmosphere, it is necessary to seal the gap between the rotating, heated kiln tube and the stationary ends containing the inlet or the outlet for the material to be treated in the rotary kiln with sealing rings. This necessity and the problems that have appeared from their practical implementation have already been described in DE 40 35 129 A1 with reference to the changing sealing gap dimensions at the periphery of the seal. This problem was solved with self-centering sealing surfaces, which engage each other with a positive fit and are thus profiled for this purpose.
Because self-centering seals must withstand considerable shear forces, their sealing behavior is less satisfactory in comparison with elastic sealing rings.
The use of comparable elastic seals requires a multi-sided support for the ring seal in a sealing groove, which has a polygonal, usually rectangular, cross section. The insertion of sealing rings in such grooves for holding sealing rings is only relatively problem-free if the sealing rings have very accurate dimensions. Until now, the problem of dimensional accuracy for such sealing rings has only been solved extremely unsatisfactorily, so that instead of annular, closed seals, prefabricated endless sealing cords have been used which are cut to length corresponding to the desired seal circumference. These sealing rings, which do not belong to the present class, have the disadvantage, among other things, that their sealing behavior at the joint is usually unsatisfactory. In addition, problems due to increased wear and tear occur at the joint.
Previous attempts at using sealing rings with polygonal, closed cross sections consisting of a core ring with a joint as well as a cover made from an endless braid have always failed in practice because the closed sealing rings too often deviate in cross section and/or in circumference from the desired dimensions. The associated waste was excessively high.
Endless sealing cords were successful to a certain degree in improving the mechanical strength and especially the shape-retention capability of braided sealing cords. For this purpose, the braid fibers in the polygon corners were made out of a different material than the braid fibers in the middle of the polygon surfaces. For example, elongated PTFE filaments impregnated with graphite were used as braid fibers in the regions of the centers of the polygon surface and aramid filaments were used in the region of the polygon corners.
For larger sealing cross sections, especially seals that consist of a core material and a braid, and especially for closed sealing rings, this braid technique, as described, e.g., in EP 0 741 807 B1, leads only under certain circumstances to the desired result, and at best up to a maximum operating temperature of 300° C.
Starting from these conditions, one object of the invention is forming an endless sealing ring for end-wall seals of rotary kilns for all operating temperatures, but especially for temperatures >400° C., such that for simpler assembly, a high degree of sealing effectiveness is guaranteed. Especially desired are small tolerances for cross section and diameter. According to the invention, rotary kiln end-wall seals should exhibit especially low wear and tear if possible and should have a service life that corresponds as much as possible to the maintenance intervals of the rotary kiln.